Many serial arbitration techniques use an open pull-down collector configuration to arbitrate between a number of devices. FIG. 2 is a block diagram that illustrates such a prior art serial arbitration system. Three processors 0 50, 1 51, and 2 52 are coupled via a common bus 54 with an open collector resistor 55. The bus is pulled up with a pull-up transistor 56 controlled by a pre-charge line 57 and it is pulled down with a pull-down transistor 58 controlled by an ARB signal 59. In order to minimize the chance of shorts, only the master processor 50 operates the pull-up transistor 56, while all processors 50, 51, 52 operate pull-down transistors 58.
In portable multi-processor systems, such as portable multi-media devices, battery lifetime is a primary concern. The need to use open collector resistor 55 increases power consumption. Indeed, the system draws static power, even when not operational. The result is that this sort of arbitration system draws too much current to be used in battery operated systems.
The system shown in FIG. 2 also has some other problems. First, it does not support dynamic priority levels without significant modifications. Even then, it does not break priority level ties. Finally, it cannot detect and properly handle the situation where errors occur during the priority arbitration phase.